1. Field of the Invention
The present invention relates to a radiographic image capturing apparatus having a scintillator for converting radiation into fluorescence, and a photodetector substrate for converting the fluorescence into electric signals.
2. Description of the Related Art
In the medical field, it has widely been customary to apply radiation from a radiation source to a subject and detect radiation that has passed through the subject with a radiation detector that makes up part of a radiographic image capturing apparatus, thereby capturing a radiographic image of the subject. The radiographic image capturing apparatus includes a scintillator for converting radiation that has passed through the subject into fluorescence, and a photodetector substrate for converting the fluorescence into electric signals. The photodetector substrate includes photodetector devices, which include photodiodes for detecting the fluorescence.
If the photodiodes of the photodetector devices are made of amorphous silicon (a-Si) or the like, then some of the electric charges (i.e., electrons) that are converted from the fluorescence become temporarily trapped by the impurity level (defect) of the amorphous silicon. If such trapped electrons are subsequently released due to a rise in temperature of the photodiodes, which may be caused at the time a moving image is captured over a long period of time, unwanted current such as dark current tends to be generated, possibly producing noise in a resultant radiographic image of the subject. To solve this problem, as disclosed in Japanese Laid-Open Patent Publication No. 2010-525359 (PCT) and Japanese Laid-Open Patent Publication No. 2007-225598, there has been proposed a light resetting process for reducing noise by applying resetting light to the photodiodes at a time that radiation is not being applied to the subject, i.e., if a radiographic image of the subject is not being captured, to thereby embed electric charges in the impurity level, so that electric charges converted from fluorescence in a case where radiation is applied to the subject, i.e., in a case where a radiographic image of the subject is captured, will not become trapped by the impurity level.
According to Japanese Laid-Open Patent Publication No. 2010-525359 (PCT), a reflective layer having a plurality of small holes therein, a scintillator, and a photodetector substrate, are arranged in this order, and resetting light is applied to light detecting elements of the photodetector substrate through each of the small holes and the scintillator. According to Japanese Laid-Open Patent Publication No. 2007-225598, a reflecting layer, a resetting light source, a scintillator, and a photodetector substrate are arranged in this order, and resetting light emitted from the resetting light source is applied to a photodetector device of the photodetector substrate via the scintillator.